Milling tools for chip-removing machining of metal workpieces are generally composed of a rotatable tool body and a plurality of replaceable cutting inserts made of cemented carbide, ceramics, or other hard material. Since the cutting inserts are subjected to significant wear upon use in a milling tool, it is desirable for the insert to have as many edges as possible in order to prolong the service life of the cutting insert. Cutting inserts are therefore often made double-sided with cutting edges formed along both an upper side and a lower side of the insert, thus doubling the number of cutting edges per insert.
A face milling tool configured for chip-removing machining and a double-sided cutting insert with seven main cutting edges per side is disclosed in EP2022584. The milling tool comprises a tool body including a front end and a rear end, between which a central rotation axis extends around which the tool is rotatable in a direction of rotation and with which an envelope surface is concentric. Several insert seats are formed in a transition between the front end and the envelope surface. Each insert seat has a bottom support surface and a side support having at least one side support surface. A chip pocket is provided in front of each insert seat in the direction of rotation of the tool. The tool further includes several cutting inserts securely and detachably mounted in the insert seats.
The cutting insert disclosed in EP2022584 has an upper side defining an upper extension plane and a lower side defining a lower extension plane parallel to the upper extension plane, wherein a center axis extends perpendicularly through the upper extension plane and the lower extension plane. A side surface connects the upper side and the lower side, the side surface comprising a plurality of main and secondary clearance surfaces. Seven identical and alternately usable upper cutting edges extend around the upper side, wherein each cutting edge comprises a chip removing main cutting edge portion and a secondary cutting edge portion, wherein the main cutting edge portion is formed in a transition between the upper side and one of said main clearance surfaces, and the secondary cutting edge portion is formed in a transition between the upper side and one of said secondary clearance surfaces in a region between two main cutting edge portions. The milling insert has a conventional negative geometry with the clearance surfaces formed at right angles with respect to the upper and lower extension planes of the insert. The cutting insert is mounted in the tool body of the milling tool such that the main cutting edge is at a corner angle of 40°-44° with respect to the axis of rotation of the milling tool. In other words, the entering angle κ between the main cutting edge and the direction of feed of the milling tool is 46°-50°. The cutting insert further has curved cutting edges, which serve to ensure a positive effective angle of inclination of the main cutting edge also for negative axial and moderately negative radial tipping-in angles (rake angles). This improves the chip formation properties of the tool for moderate cutting depths. However, the effective angle of inclination is, even with the curved cutting edges, only moderately positive. Drawbacks associated with small effective angles of inclinations, such as cutting characteristics with regards not only to the chip formation and control but also to the toughness behaviour of the cutting edges and the noise level of the tool, are therefore present with a cutting insert and a milling tool disclosed in EP2022584.